1. Field of the Invention
The present invention relates to a method of controlling a sound source for an electronic musical instrument and an electronic musical instrument which simulates an acoustic instrument such as a wind instrument, a rubbed string instrument (a bowed instrument), or the like and, more particularly, to an improvement with which a sound source circuit can always normally generate tones on the basis of input data such as positions or pressures corresponding to musical tone parameters from a performance operation member.
2. Description of the Prior Art
An electronic musical instrument which generates performance tones of a rubbed string instrument such as a violin or of a wind instrument such as a clarinet comprises a physical sound source (physically modelled sound source) for generating electronic tones obtained by physically approximating tones generated by mechanical vibrations of a string corresponding to movement of a contact between a string and a bow, or air vibrations in a mouthpiece of a wind instrument using an electrical circuit. In an electronic musical instrument of this type, pitch data of an ON key is inputted upon operation of a keyboard, and a parameter control signal corresponding to a bow pressure or a bow velocity of a bowing operation, a breath pressure or an embouchure of a blowing operation is inputted to a sound source by a performance operation member comprising, e.g., a slide volume, thereby generating and producing an electronic tone.
In a conventional electronic musical instrument, a musical tone control signal based on an operation position or an operation pressure of a performance operation member is merely multiplied with a given coefficient regardless of a velocity or pressure region, and is substantially directly inputted to a sound source.
However, when operation data of a performance operation member is directly inputted to a sound source, a tone cannot be generated or an irregular or abnormal tone such as an uncomfortable tone or a so-called falsetto tone is generated in a given operation region. Therefore, the performance operation member must be operated while avoiding generation of these irregular or abnormal tones. Thus, an electronic musical instrument is not easy to play.
The irregular tones are generated for the following reason. As for a bowed instrument, an irregular tone is generated since it does not fall within a regular tone generation region in view of the relationship between parameters of a bow pressure and a bow velocity. The relationship between a bow pressure and a bow velocity of a bowed instrument is roughly divided by four straight lines passing the origin into a regular or normal tone generation region A where a tone begins to sound, a tone duration (or tone sustaining) region B where a generated tone is sustained, and an irregular or abnormal tone region C where a tone is muted or an uncomfortable tone is generated, as shown in FIG. 2. Therefore, when a performance operation member is operated in a state corresponding to a given bow velocity v.sub.1, if a bow pressure at that time is too high or too low and cannot fall within the tone generation region A, a tone cannot begin to sound. If a tone enters the irregular tone region C, a tone is muted or an uncomfortable tone or a falsetto tone is generated.
In a conventional electronic musical instrument, since operation data of a performance operation member is substantially directly inputted to a sound source, the data may enter the irregular tone region depending on an operation state, and in this case, a tone is muted or an uncomfortable tone is generated.